1. Field of the Invention
This invention is concerned with pre-engine catalytic converters for use with fuel systems containing some oxygenated organic compounds mixed with liquid hydrocarbon fuel. In particular it is concerned with increasing the octane number and the heating value of the fuel so as to improve both the performance and the fuel economy of the system.
2. Description of the Prior Art
The blending of alcohols, ethers, esters and the like with hydrocarbon fuels for the purpose of increasing the octane number of said fuel is well known in the art. For instance, U.S. Pat. No. 3,904,384 discloses a high octane gasoline produced by mixing suitable hydrocarbons with t-butyl isopropyl ethers; U.S. Pat. No. 3,903,251 mixes butyl alcohol and butyl acetate with hydrocarbons; and U.S. Pat. No. 3,901,664 blends t-butyl alcohol, isopropyl alcohol and methyl alcohol with hydrocarbons to produce high octane motor fuel. These fuels typically contain as much as 40% of oxygenated compounds in the blend to increase the octane number of the gasoline to a level competitive with that of gasoline containing tetraethyl lead, an octane booster in commercial fuels. However, although many oxygenated organic compounds have high octane ratings and are able to impart increased anti-knock properties to hydrocarbon motor fuels and some of them, such as methanol, have been proposed for use as fuels by themselves, they have very poor fuel economy characteristics relative to petroleum gasolines. By using a pre-engine converter system as embodied herein the advantages derivable from oxygenates can be realized without sacrificing fuel economy.
An additional advantage of the system of this invention is that it overcomes the cold-start problems encountered with pre-engine catalytic converters which are designed to crack low octane normally liquid hydrocarbons to light, normally gaseous, higher octane hydrocarbon fuel. The primary problem is that when one is first starting an engine, in an automobile for instance, there is not sufficient heat available to bring the cracking catalyst up to the temperature required to induce the desired reaction. In addition, the cracking reaction is endothermic. The result, of course, is that the gasoline that reaches the engine is just as low in octane number as it was before entering the pre-engine converter and engine performance is very poor until it warms up enough to heat the catalyst to cracking temperature. Very elaborate procedures have been proposed to overcome the problem, including the use of two separate fuel systems, electric warm-up of the catalyst utilizing the energy stored in the car battery and pre-combustion of a portion of the fuel within the catalytic converter, but they all have features which make them undesirable or impractical.